Combined diffuser gap and fuse for transformer protection



Jan. 22, 1935. c w DIEHL 1,988,683

COMBINED DIFFUSER GAP AND FLISE FOR TRANSFORMER PROTECTION Filed Oct. 14, 1953 LT/zenfially responsive? WITNESSES: INVENTOR U Y E Carl W Dz'ehl- ATTORNEY Patented Jan; 22, 1935 PATENT OFFICE COMBINED DIFFUSER GAP AND FUSE FOR TRANSFORMER PROTECTION Carl W. Diehl, Sharon, Pa.,

assignor to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa.,

a corporation of Pennsylvania Application October 14, 1933, Serial No. 693,624

2 Claims.

My invention is an improvement on that which is shown and described in an application of J.

K. Hodnette for a Surge and outage-proof distribution transformer, Serial No. 688,803, filed 6 September 9, 1933, assigned to the Westinghouse Electric 8: Manufacturing Company.

The Hodnetteinvention relates to a distribution transformer which is provided with means, including a diffuser gap element, for completely protecting the windings against excess voltage surges, and further provided with a combined thermal and over-current protector mounted in the transformer tank and electrically associated with the secondary leads of the transformer for affording protection both against overheating and external short-circuits on the secondary line, and still further provided with a high-voltage fuse mounted inside of the transformer tank and electrically connected inside of the connections of the diffuser gap device, for protecting the primary supply line against short-circuit due to an internal fault in the transformer, the fuse being so connected that it is not traversed by the surge currents which are discharged by the diffuser gap device. The diffuser gap device contains means for evolving a large quantity of substantially non-ionized gas under the direct action of an arc, and venting means are provided for discharging this gas outside of the trans- 30 former tank, so as to quickly extinguish the arc in the diffuser gap device.

My invention is directed to a combination of the diffuser gap device and the high-voltage fuse element, the latter being disposed in a fuse-discharge chamber which is vented through the diffuser chamber so as to discharge its gases outside of the transformer tank.

My invention is shown, by way of example, in the accompanying drawing, in which:

Figure 1 is a diagrammatic view of circuits and apparatus showing my invention in a distribution transformer; and

Fig. 2 is a cross-sectional view of my combined diffuser and fuse device.

As shown in Fig. 1, my invention is applied to a distribution transformer which comprises a conducting tank or casing 1 containing a highvoltage primary winding 2 and a low-voltage secondary winding 3. High-voltage leads 4 extend out from the terminals of the high-voltage winding 2 and pass, through the transformer casing 1 through suitable insulating bushings 5. Low-voltage phase-leads 6 and-usually also a low-voltage neutral lead 7 extend out from the terminals and mid-point, respectively, of the low-voltage winding 3 and pass through the walls of the casing 1 through suitable bushings 8 and 9. The casing is either solidly grounded, or, preferably as shown, grounded through a discharge-gap device 11.

My combined diffuser and fuse element is indicated generically at 12 and comprises a diffuser element 13 and a fuse element 14. The diffuser element 13 comprises an insulating enclosing tube 15 which is preferably made of fibre, sometimes known as hard fibre, which has the quality of evolving large quantities of non-conducting gas under the direct influence of an arc. At the ends of the enclosing tube 15 are disposed conducting terminal electrodes 16 and 1'1,

respectively, both of which are shown as being hollow. These electrodes constitute the ter-' minals of the discharge gap. The space between the two electrodes is nearly filled by a diffuser proper, indicated at 18, which consists of a multi-slotted fibre plug which is fitted within the casing or insulating tube 15, and abuts with one end against the terminal electrode 16, the other end being spaced from the other terminal electrode 17 by means of a separate fibre or other insulating spacer-tube 19. The second electrode 17 preferab y has a protuberance 21 extending inwardly within the spacer tube 19 so as to help direct thearc into the slots of the diffuser 18.

The first electrode 16 of thediifuser element is mounted within a perforation 22 in the wall of the transformer-casing 1 so as to vent the gas outside of the diffuser chamber. The second electrode 17 of the diffuser element is connected to the incoming high-tension lead 4 just after it comes into the tank through the bushing 5.

The fuse element 14 is mounted integrally with the diffuser element 13, as a continuation thereof, comprising a fuse-enclosing fibre tube 24 which is screwed into the second electrode 17 of the diffuser element. The free end of the fuse-enclosing fibre tube 24 is closed by means of a terminal electrode 25 which is connected to a continuation of the high-voltage lead 4, as indicated at 26, the same being electrically connected to the terminal of the highvoltage winding 2. A fuse link 27 is disposed within the fuse-enclosing fibre tube 24, said link being connected at its terminals to washers 28 and 29, respectively. It will thus be seen that when the fuse melts, the evolved gases will be discharged through the diffuser chamber o the outside of the tank or casing 1.

The distribution transformer is so designed that the insulation of the windings 2 and 3 will have an impulse strength which is safely in excess of the fiashover value of the bushings with which they are associated, so that the bushings will flash over before the winding insulation will fail. The bushing-9 of the neutral lead 7 is usually provided with preferred-gap means, which may be a small set-screw 31, as illustrated in Fig. 1, for providing a preferred discharge path from the casing to the neutral lead 7, which is usually grounded outside of the tank, as indicated at 32. The discharge gap 11 is usually set to flash over at a still lower voltage than the neutral bushing 9, so that the normal discharge will be from the incoming high-voltage lines to the diffuser element 13, thence to the casing 1, and thence through the discharge gap' 11 to ground. The diffuser element 13 is adjusted to break down before the associated high-voltage bushing 5 will fail. In

this way, the transformer is fully protected against failure due to high-voltage surges.

The transformer is protected against external short-circuits on the secondary or low-voltage winding, and also against over-heating due to sustained or oft-repeated overloads, by means of a circuit breaker 34 which is both thermally- ,responsive and current-responsive, being normally thermally-responsive for usual overload conditions of from one and one-half to three times the normal load, but becoming current-responsive in the event of extremely severe over-currents which occur when there is a dead short-circuit on the secondary lines, said overcurrents being of the order of ten to forty times the normal load current. In this way, the transformer is protected against overheating and against secondary short-circuits.

The fuse link 27 of the fuse element 14 is of such size as to afford protection against an internal failure of the transformer, which would amount to a short-circuit on the incoming highvoltage lines 3'7.

I claim as my invention:

1. A transformer comprising insulated windings, and a conducting casing, primary and secondary leads extending out from the windings through the casing, a protective device constituting a combined diffuser and fuse device mounted within the transformer-casing, the diffuser having an enclosing tubular insulating member defining a difiuser chamber, terminal electrodes at the respective ends of said diffuser chamber, means for venting said difiuser chamber outside of the transformercasing, and arc-responsive gas-evolving means in said diffuser chamber, and the fuse device having a tubular'insulator comprising a fuse-discharge chamber, means including said diffuser chamber for venting said fuse-discharge chamber outside of said transformer-casing, and a fusible link disposed in said fuse-discharge chamber, and electrical connections for connecting said terminal electrodes of the diffuser between a primary lead and the transformer-casing and for connecting said fusible link between said lead and a winding-terminal of said transformer so that the currents discharged by said difiuser do not pass through said fusible link.

2. A protective .gap device comprising a unitary structure constituting a combined diffuser and fuse device, the diffuser having an enclosing tubular insulating member defining a difiuser chamber, terminal electrodes at the respective ends of said diffuser chamber, means for venting said diffuser chamber, and arc-responsive gasevolving means in said diffuser chamber, and the fuse device having a tubular insulator comprising a fuse-discharge chambenm'eans including said diffuser chamber for venting said fusedischarge chamber, and a fusible link disposed in said fuse-discharge chamber.

CARL W. DIEHL. 

